Cooperative Effect of Anion and Mole Ratio on the Coordination Modes of an NO₂S₃‑Donor Macrocycle

Synthesis of an NO₂S₃-macrocycle (<b>L</b>) incorporating a pyridine subunit and its anion and/or mole ratio-dependent coordination modes in the formations of mercury­(II) complexes is reported. When the mercury­(II) salts with different anions (ClO₄^– or Br^–) were reacted with <b>L</b>, the Hg­(ClO₄)₂ afforded a typical endocyclic complex [Hg<b>L</b>]­(ClO₄)₂ (<b>1</b>). Meanwhile, the HgBr₂ gave an exocyclic complex [Hg<b>L</b>Br₂] (<b>2</b>) in which the metal ion exists outside the macrocyclic cavity. The observed anion effect on the coordination modes can be explained by the anion coordination ability toward the metal cation. In the mole ratio variation experiments, notably, the use of 1.5 equiv or above of HgBr₂ in the same reaction condition gave a unique endo/exocyclic dumbbell-type complex <b>3</b>, [Hg₄<b>L</b>₂Br₆]­[Hg₂Br₆]. However, the formation of the endocyclic Hg­(ClO₄)₂ complex <b>1</b> shows no mole ratio dependency. To monitor the observed mole ratio-dependent exocoordination products as well as their reactivities and reversibility, systematic powder X-ray diffraction (PXRD) analysis was also applied. From single crystal X-ray and PXRD analyses, it was found that endocyclic complex <b>1</b> is not reactive, but complexes <b>2</b> and <b>3</b> are reactive and show the reversibility between them in the presence of the corresponding reactants